[QE-users] vc-md simulation: Pressure stays below target

[Kazume NISHIDATE]

Dear Seitaro Yazawa,

Here is the quickly computed result using your input file. The vertical axis represents pressure (kbar), and the horizontal axis represents the MD time steps.


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Pressure fluctuates around zero kbar, with an amplitude of ?100 kbar (10 GPa). This is a typical result for an MD computation with such a small system, comprising 80 atoms in total, at a temperature of 300 K. The reason for this was described in my previous email.

Note that I used only the 35 Ry for cutoff energy, and only the gamma point is used for reciprocal space integration. 

To restrain the fluctuations, there are two strategies. One approach is to increase the number of atoms in the calculation, for example, to 1000. The other approach is to perform the MD computation multiple times and average the pressure variations across these computations, thanks to the Ergodic theorem.


Good luck with your computation :)


Sincerely yours,


> 2025/07/16 18:50?Seitaro YAZAWA <seitaroyazawa at eps.s.u-tokyo.ac.jp>????:
> 
> Dear Nishidate,
> 
> Thank you for your reply.  Following your advice, I will give it a try. 
> 
> Seitaro Yazawa
> graduate student
> Department of Earth and Planetary science
> Univ. Tokyo
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????
Kazume NISHIDATE Ph.D

Department of Systems Innovation Engineering,
Graduate School of Science and Engineering, Iwate University
4-3-5 Ueda, Morioka, Iwate, 020-8551 JAPAN
Phone:+81-19-621-6391
kazume.nishidate at gmail.com, nisidate at iwate-u.ac.jp
https://sites.google.com/site/nisidatelab/